In the past, electronic equipment such as a cellular phone, a notebook PC, etc., is provided with a key substrate having key parts, and further with a switch module which is arranged in opposition to the key substrate so as to change over between the on and off states of an electric connection according to the contact and non-contact of a key top. In FIG. 5, there is shown a schematic perspective view of a conventional switch module 100 which is arranged in opposition to a key substrate 80 having a plurality of key parts 70. In addition, in FIG. 6, there are shown schematic cross sectional views of the switch module 100 illustrated in FIG. 5.
As shown in FIG. 6(a), the switch module 100 is provided with metal domes 50 each having electrodes 55 contained therein, a circuit substrate 60, a light guiding member 30, and LEDs (Light Emitting Diodes) 20 as light emitting devices. The metal domes 50 are integrally held on the circuit substrate 60 by means of a metal dome sheet 40, and the light guiding member 30 is mounted on the metal dome sheet 40 at a predetermined distance or interval formed therebetween by means of an adhesive layer 35. In addition, on a lower surface of the light guiding member 30, there are formed a plurality of light scattering processed parts 30a, which have been subjected to prism processing, or printing processing in which white ink is printed in a dot-like manner, or the like, and between the light guiding member 30 and each LED 20, there is arranged a reflector (reflection member) 25 for introducing the light emitted from the LED 20 into the light guiding member 30 from one end thereof in an efficient manner.
According to such a construction, it becomes possible to change over between the on and off states of a switch by electrical contact and non-contact between each metal dome 50 and the corresponding electrodes 55 due to a deformation of the metal dome 50 caused by a corresponding key part 70 being pushed down, and at the same time, the light guiding member 30 is arranged on a back surface of the key substrate 80, i.e., between the key substrate 80 and the metal dome sheet 40, so it becomes possible to illuminate the individual key parts 70 from the interior of the light guiding member 30 by causing the light, which has been emitted from each LED 20 and has entered the light guiding member 30, to be scattered by the light scattering processed parts 30a. Here, note that related techniques are disclosed in a first through a sixth patent document, as listed below.